My truck throttle surges at random really bad after puttin the new lift pump on a couple days ago. That was the second time iv driven it over 50mph since install ..my buddy said it's just stuck air bubbles and that his throttle surged for about a week .. Normal?

 

Nope, not normal at all - I've had my fuel system open gazillion times, never had a surge for more than a minute, if that. Are you sure the line between the lift pump and the filter head is seated and sealed properly on both ends? Altho that would result in a fuel leak, while what you have going on sounds more like an air intrusion between the tank and the lift pump somewhere...

 

Yes I'm sure .. And it doesn't surge longer than a minute it's random and only about one time per trip

 

Or the rubber hose between the tank hard line and lift pump ...

It's starving for fuel, Likely sucking air between lift pump and tanks.

-Enjoy
fh : )_~

 

but its RANDOM fellas not constant .. if it was a hose problem it would be constant id imagine ??

 

Nope ...

-Enjoy
fh : )_~

 

hmm .. ok ill check into it a lil further but isnt it possible an air pocket could be stuck somewhere?

 

nah,once shes running the air will purge in just a few seconds.
see,the fuel runs continually through the system.whatever is not used by the engine cools the fuel system and returns to the tanks.
(this causes condensation by the way,and is why a water separator is very important.)
for you to have a problem while running,means more is being let in.
it's hard for the stock puller to pull fuel with an air leak on its suction side,and it will cause your trouble.

 

The pump is irrelevant ... A leak on the suction side introduces air into the fuel stream.

Just because fuel is not seen leaking does not mean there is no leak!
Air is smaller then fuel, thus it can leak air and not fuel!

What you are describing is starvation, either from air in the fuel or inadequate flow.

Did you replace the rubber hose from the frame to the lift pump when you replaced the lift pump ???

-Enjoy
fh : )_~

 

Maybe the new working lift pump sucked up a lot of crap from the tank and clogged the fuel filter already.

I think some Diesel Kleen in the tank and a new fuel filter should fix it.

 

How come fuel starvation or air intrusion will cause the truck to surge?

 

My truck does this too, but when mine surges, it rattles like it does when the timing advance is on and it will pick up about 5-6 mph, it doesn't usually last long. Does this happen to yours too 84?

 

A diesel's RPM is controlled by the amount of fuel it burns... Less fuel less RPM's, More fuel more RPM's.

Unlike a gasser that controls air and fuel.

-Enjoy
fh : )_~

 

IIRC the IP uses the fuel pressure at its inlet to adjust injection timing, when the fuel system sucks air in that drops the inlet pressure temporarily thus causing the mechanism to advance further than it normally would. Advanced timing can have that power surge effect you're experiencing, but if it gets too advance bad things can happen to the engine.

 

No, The IP relies on the lift pump pressure for nothing other then providing fuel ... The return system makes it kinda like pouring fuel into an open container.

Yes, If you were to block the returns, pump up the pressure inside the IP it will affect the timing, in an uncontrolled manner. And likely destroying the IP.

Air in the fuel means less fuel in the cylinder, less fuel in the cylinder, less RPM's, thus the surge ...

-Enjoy
fh : )_~